CONSIDERATIONS ON COLOURS. 1 15 



wo effays, where he has treated the fubject in a very pleating 

 manner.* 



Mr. Prieur thinks, that Ihofe appearances of the folar light alfo light 

 received through a hole in a coloured curtain, which General loured curt "* 

 Meufnier had remarked on account of their Angularity, are tain j 

 alio to be afcribed to contrail. With this too he affimilates°P al s j 

 feveral cafes of colours difplayed by opals, or, to fpeak more 

 generally, by bodies including perceptible opake parts dtffe- 

 minated through a tranfparent fubflance. In the fame way olddufton paper 

 he explains the colours under which the grayith dull collected ° ' 

 by age on papers, or oh coloured fluffs, appears; and he and bluenefs of 

 draws the fame inferences with refpecl to the blueifh appear- c e veins » 

 ance of the veins of the human body. 



Helikevvife propofes a new method of rendering the colours 

 of contrafl very fenfible, more fo than even by the known 

 procefs of accidental colours, and nevertheleis without occa- 

 (ioning any extraordinary fatigue of the eye. This lad circum- 

 stance is of no fmall confequence, for every one mud be aware, 

 that fo delicate an organ cannot be flrained by over exertion 

 without danger. 



This method confifts, the obferver being in a room with a Method of ren- 

 good light, in placing againil the window the coloured papers, ^r^lenSe!** 3 

 on which he means to obferve the contrails in the manner above 

 mentioned. The coloured paper ferving as the ground will 

 then poflefs a degree of femitranfparency, while the little ilip of 

 a different colour placed upon it is more opake, and in the 

 fthade, on account of the double thicknefs of paper: thus 

 the colour produced by the contrafl is rendered much more 

 flriking. 



From this arrangement loo refults the Angularly linking Slip of white 

 effect of contact of a little flip of white paper applied fuc- f^£j°p a p e ° r " 

 celfively on paper, glafs, and cloth of a given colour. When glafs, &c 

 the tranfparent body is red, the opake white appears blueilh 

 green; if the ground be orange, it is decidedly blue; 6n a 

 yellow ground, a kind of violet ; on a crimfon ground, 

 green, &c. ; always correfponding exactly to the complementary 

 colour. 



On this it mull be obferved, that, according to the rule al- Explanation, 

 ready mentioned, if we abflract from white, which is a com- 



* See his Philofophical Works, Vol. I, p. 319, and following. 

 I 2 pound 



